 #define _CRT_SECURE_NO_WARNINGS 1

class Solution {
public:
    typedef pair<int, int> PII;
    int dx[4] = { 0, 0, -1, 1 };
    int dy[4] = { 1, -1, 0, 0 };

    vector<vector<int>> floodFill(vector<vector<int>>& image, int sr, int sc, int color) {
        int prev = image[sr][sc];
        if (color == prev) return image;
        int m = image.size(), n = image[0].size();

        queue<PII> q;
        q.push({ sr, sc });

        while (!q.empty())
        {
            auto [a, b] = q.front();
            image[a][b] = color;
            q.pop();

            for (int i = 0; i < 4; i++)
            {
                int x = a + dx[i], y = b + dy[i];
                if (x >= 0 && x < m && y >= 0 && y < n && image[x][y] == prev)
                    q.push({ x, y });
            }
        }

        return image;
    }
};

class Solution {
public:
    int dx[4] = { 0, 0, -1, 1 };
    int dy[4] = { 1, -1, 0, 0 };
    vector<vector<bool>> vis;
    int m, n;

    int numIslands(vector<vector<char>>& grid) {
        m = grid.size(), n = grid[0].size();
        vis = vector<vector<bool>>(m, vector<bool>(n));
        int ret = 0;

        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (grid[i][j] == '1' && !vis[i][j])//只要找到一个1，便从这个位置周围找其他的1
                {
                    ret++;
                    //标记这整块陆地
                    bfs(grid, i, j);
                }
            }
        }

        return ret;
    }

    void bfs(vector<vector<char>>& grid, int i, int j)
    {
        queue<pair<int, int>> q;
        q.push({ i, j });
        vis[i][j] = true;

        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();

            for (int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1' && !vis[x][y])
                {
                    q.push({ x, y });
                    vis[x][y] = true;
                }
            }
        }
    }
};

class Solution {
public:
    int dx[4] = { 0, 0, -1, 1 };
    int dy[4] = { 1, -1, 0, 0 };
    bool vis[51][51];
    int m, n;


    int maxAreaOfIsland(vector<vector<int>>& grid) {
        m = grid.size(), n = grid[0].size();
        int ret = 0;
        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (grid[i][j] == 1 && !vis[i][j])
                {
                    ret = max(ret, bfs(grid, i, j));
                }
            }
        }

        return ret;
    }

    int bfs(vector<vector<int>>& grid, int i, int j)
    {
        queue<pair<int, int>> q;
        q.push({ i, j });
        vis[i][j] = true;

        int count = 0;
        count++;
        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();

            for (int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == 1 && !vis[x][y])
                {
                    q.push({ x, y });
                    count++;
                    vis[x][y] = true;
                }
            }
        }

        return count;
    }
};

class Solution {
public:
    int m, n;
    int dx[4] = { 0, 0, -1, 1 };
    int dy[4] = { 1, -1, 0, 0 };

    void solve(vector<vector<char>>& board) {
        m = board.size(), n = board[0].size();

        //1.将边缘的O修改为.
        for (int i = 0; i < m; i++)
        {
            if (board[i][0] == 'O') bfs(board, i, 0);
            if (board[i][n - 1] == 'O') bfs(board, i, n - 1);
        }

        for (int j = 0; j < n; j++)
        {
            if (board[0][j] == 'O') bfs(board, 0, j);
            if (board[m - 1][j] == 'O') bfs(board, m - 1, j);
        }

        //2.将.变回O，将O变换为X
        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (board[i][j] == '.') board[i][j] = 'O';
                else if (board[i][j] == 'O') board[i][j] = 'X';
            }
        }
    }

    void bfs(vector<vector<char>>& board, int i, int j)
    {
        queue<pair<int, int>> q;
        q.push({ i, j });
        board[i][j] = '.';

        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            for (int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'O')
                {
                    q.push({ x, y });
                    board[x][y] = '.';
                }
            }
        }
    }
};